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Method for battery cold-temperature warm-up mechanism using cell equilization hardwareMethod for battery cold-temperature warm-up mechanism using cell equilization hardware description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060238165, Method for battery cold-temperature warm-up mechanism using cell equilization hardware. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] This invention relates generally to multi-cell lithium chemistry battery systems, and, more particularly, to a method and apparatus for operating such battery systems. [0003] 2. Description of the Related Art [0004] Rechargeable, multi-cell battery systems are known and have been based on various chemistries including lead acid (PbA), nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (LiIon) and lithium polymer (LiPo). A key performance aspect of each battery technology relates to how charging (and overcharging) is accomplished, and how inevitable cell imbalances are addressed. [0005] Conventionally, cell-to-cell imbalances in lead-acid batteries, for example, have been solved by controlled overcharging. Lead-acid batteries can be brought into overcharge conditions without permanent cell damage, inasmuch as the excess energy is released by gassing. This gassing mechanism is the natural method for balancing a series string of lead acid battery cells. Other chemistries, such as NiMH, exhibit similar natural cell-to-cell balancing mechanisms. [0006] Lithium ion and lithium polymer battery chemistries, however, cannot be overcharged without damaging the active materials. The electrolyte breakdown voltage is precariously close to the fully charged terminal voltage. Therefore, careful monitoring and controls must be implemented to avoid any single cell from experiencing an over voltage due to excessive charging. Because a lithium battery cannot be overcharged, there is no natural mechanism for cell equalization. [0007] Even greater challenges exist depending on whether the battery system is a single cell or multiple cells. Single lithium-based cells require monitoring so that cell voltage does not exceed predefined limits of the chemistry. Series-connected lithium cells, however, pose a more complex problem; each cell in the string must be monitored and controlled. Even though the system voltage may appear to be within acceptable limits, one cell of the series string may be experiencing damaging voltage due to cell-to-cell imbalances. Based on the foregoing, without more, the maximum usable capacity of the battery system may not be obtained because during charging, an out-of-balance cell may prematurely approach the end of charge voltage and trigger the charger to turn off (i.e., to save that cell from damage due to overcharge as explained above). [0008] One approach taken in the art to address the foregoing problem involves the concept of cell balancing. Cell balancing is useful to control the higher voltage cells until the rest of the cells can catch up. In this way, the charger is not turned off until the cells reach the end-of-charge (EOC) condition more or less together. More specifically, the cells are first charged, and then, during and at the end-of-charging, the cells are balanced. [0009] One example of a cell balancing approach involves energy dissipation. A shunt resistor, for example, may be selectively engaged in parallel with each cell. This approach shunts the excess energy as each cell reaches an end-of-charge condition, resulting in the system becoming more active as the cells reach full charge. During the moments preceding full charge in a system with n total cells, (n-1) cells are dissipating equalization energy as the last cell approaches end-of-charge. This condition results in a buildup of waste energy in the form of heat, which can trigger thermal controls (i.e., discontinuing the charging temporarily until the temperature comes down). These controls extend the overall charge time for the battery system. [0010] Another problem to be solved is that for lithium chemistry battery types, normal charging currents, when applied at low temperatures, can damage the cells. "Normal" in this regard corresponds to the level of current a lithium battery can accept at standard operating temperature (e.g., 20.degree. C.-68.degree. F.). Low temperature charging can cause lithium metal plating to occur, which consumes and/or damages the internal active elements of the battery. [0011] Methods are known to control battery charging at low temperatures. One such method includes the most obvious, that is, not allowing charging at low temperatures. Another known method includes the use of a separate heating device, such as a heating blanket, to warm the battery to operational temperatures. [0012] Accordingly, there is a need for a method and apparatus for operating a battery system that minimizes or eliminates one or more of the problems as set forth above. SUMMARY OF THE INVENTION [0013] One advantage of the present invention is that it allows for the low temperature charging of a lithium battery system without the need for a separate heating element. [0014] These and other features, advantages, and objects are achieved by a method of operating a battery system in accordance with the present invention. [0015] In a first aspect of the invention, a lithium battery system is provided. The battery system has a plurality of cells, a dissipative balancing circuit, a temperature sensor, and a battery controller. The balancing circuit is associated with at least one of the plurality of cells and is operable to dissipate charge of the at least one cell (e.g., in the form of heat). In a preferred embodiment, the balancing circuit includes a resistor. The temperature sensor is configured to generate a temperature signal indicative of the temperature of the at least one cell. The battery controller is configured to engage the balancing circuit when the temperature is below a first predetermined level. Turning on the balancing circuit is operative to produce heat which can be used to warm the cell(s), raising the temperature to a level suitable for charging, for example. [0016] In one embodiment, the system includes a balancing circuit for each cell, wherein the controller is configured to engage one or more of such balancing circuits. The controller is configured to discontinue engagement of the balancing circuit(s) when the temperature reaches a second predetermined level, a level suitable for charging operations. BRIEF DESCRIPTION OF THE DRAWINGS [0017] The present invention will now be described by way of example, with reference to the accompanying drawings. [0018] FIG. 1 is a schematic and block diagram view of a multi-cell battery system according to the present invention. [0019] FIG. 2 is a state of charge (SOC) versus temperature graph showing various operating regions of the present invention. [0020] FIG. 3 is a flowchart showing a process for cold temperature warm-up according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Continue reading about Method for battery cold-temperature warm-up mechanism using cell equilization hardware... Full patent description for Method for battery cold-temperature warm-up mechanism using cell equilization hardware Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for battery cold-temperature warm-up mechanism using cell equilization hardware patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Method for battery cold-temperature warm-up mechanism using cell equilization hardware or other areas of interest. ### Previous Patent Application: Desktop charger for a portable electronic device with a display Next Patent Application: Charge control device Industry Class: Electricity: battery or capacitor charging or discharging ### FreshPatents.com Support Thank you for viewing the Method for battery cold-temperature warm-up mechanism using cell equilization hardware patent info. IP-related news and info Results in 0.22786 seconds Other interesting Feshpatents.com categories: Software: Finance , AI , Databases , Development , Document , Navigation , Error 174 |
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